1. Field of the Invention
This invention relates to a device for the collection and separation of two-phase liquids such as blood. Optionally, the same device can be used to dispense the serum so separated.
2. State of the Prior Art
Of the many devices available to provide blood serum for analysis, the one which has become the norm is the evacuated container. This is simply a partially evacuated glass tube openable at one end except for a septum placed there. One particularly useful improvement of such an evacuated container comprises such a glass tube with a movable plug contained within the tube. The plug is preferably a silica gel, with or without a plastic cup-like mandrel positioned with its open end pointed to the septum. By reason of the vacuum, collected blood is easily drawn into the container. The container is then spun about a centrifuge axis adjacent to the septum end, and the gel by reason of its selected specific gravity works up to the serum-cell interface where it plugs the container against remixing of the serum and cells. An example of such a container without the mandrel is shown in U.S. Pat. No. 3,852,194.
Although such a device is useful in separating the serum from the cells, it has not avoided transfer difficulties after the serum is separated. That is, after centrifuging, the serum is commonly poured off into yet another container for the desired clinical testing. All such transfer operations are time consuming, requiring either hand processing or complicated, expensive automatic handling. Furthermore, whenever there is a transfer of a liquid sample to a separate, open container, the sample is aerated and CO.sub.2 loss or gain can occur. There is also the danger of improper transfer, either by the use of the wrong container, by the improper patient labeling of the new container, or by both. Still further, contamination of the serum by foreign materials can occur, including, for example, contamination by blood cells collected at the septum-container interface prior to centrifuging, a condition known as "blood-ring contamination."
Still other drawbacks concerning evacuated containers are that the rapid intake tends to cause hemolysis by reason of the high shear rate, particularly when flow is through reduced diameters; the vacuum can cause collapse of the patient's vein; and occasionally the containers become "flat", i.e., they lose their vacuum. In such a case of a "flat" container, the broken seal is generally insufficient to create a truly vented configuration, so that the hydrostatic pressure of the veins from which the blood is drawn encounters back pressure, and the rate of fill is insufficient. When the container is formed from solid glass, it is not possible prior to actual use to determine the loss of vacuum merely by visual inspection, and the result is that the patient has to wait while the technician looks for a new container.
Evacuated containers have, in some instances, included inorganic fillers in the compartment that collects the blood sample. A mechanical phase separator causes the filler to collapse during centrifuging. U.S. Pat. No. 3,929,646 is illustrative of such a device. However, such filler is positioned therein solely to act as a blood-clotting agent, and must be only loosely packed to allow the gel portion of the phase separator to move through it. Because the draw of the blood is provided by the vacuum, there is no attempt to use the filler as a capillary assist. As a result, the filler does not overlap with the terminus of the cannula -- that is, it is not in contact with the blood as it leaves the cannula. Instead, the filler extends from the cell-collecting portion of the compartment to a location falling far short of the mechanical phase separator and therefore, of the penetratable closure means or septum.
Flexible containers have been used to collect whole blood; and, by reason of their flexibility, they may have capillary passageways somewhere defined when the walls are collapsed. However, the collapsed wall condition is designed not to fill the containers by capillary action, but rather either to create a vacuum which causes filling of the container, as shown for example, in U.S. Pat. No. 3,513,829, or to indicate whether desired arterial blood as opposed to undesired venous blood is being collected, as shown for example in U.S. Pat. No. 3,785,367.
U.S. Pat. No. 3,867,923 is representative of blood collection bags which are completely collapsed along their entire length, and which therefore initially provide a capillary passageway along their entire length. However, such devices lose their effective capillary as soon as blood enters. Because they are not vented to the atmosphere, they require the patient's blood pressure to expend the device into its full volume. They cannot be used to collect non-pressurized blood.
Blood flow devices having capillary restrictions at a portion intermediate the ends thereof have been constructed not for the purpose of collecting blood and for separating serum, but rather for blood cell counting, as shown for example, in U.S. Pat. Nos. 2,369,577; 2,779,232; 2,807,416 and 2,875,666.
Patents disclosing a capillary passageway forming at least a part of a blood collection system include U.S. Pat. Nos. 3,645,252; 3,640,267; 3,898,982; and 3,926,521. However, these have not been suited for the use with venous collection, have been too reduced in capacity, and/or have lacked the optional capability of providing a dispensing of serum separated within the compartment.
Patents relating generally to the background of blood or other liquid collection include for example U.S. Pat. Nos. 3,513,829; 3,610,226; 3,814,079; 3,867,924; 3,897,340; 3,909,419; 3,920,557; 3,931,010; 3,938,957; 3,938,958; 3,452,601; 3,496,777; and 3,511,570.